Hawaii's Kilaueavolcano has erupted, causing lava to spew out of cracks in the ground in residential areas and prompting thousands of people to flee.

The Pacific island state's governor signed an emergency proclamation releasing disaster funds to the Big Island in the eruption's wake.

Local news footage showed streams of lava snaking through a forest and authorities reported "steam and lava emissions from a crack in Leilani Subdivision in the area of Mohala Street" following the blast.

Residents of that impacted area, some 1,700 people, were under mandatory evacuation after the burst from Kilauea, one of the most active volcanos in the world.

In addition to the obligatory evacuations, many areas fell under voluntary evacuation zones, affecting some 10,000 people, according to a local official.

US Geological Survey authorities of the Hawaiian Volcano Observatory unit were both on the ground and headed into the air to assess the eruption.

It followed some 100 small earthquakes in recent days and began around 4.45 pm local time (2.45am GMT Friday), according to the agency.

Earlier, at 10.30 am, a larger 5.0-magnitude earthquake south of the Puu Oo volcano cone triggered rockfalls and potential collapse into a crater on the volcano, according to USGS.

Big Island resident Janice Wei said she felt "a big shake underneath my feet" and then said immediately after she saw a giant pink plume of smoke.

"We've been waiting for big movement from the crater, after so many small earthquakes," she added.

Using his drone, resident Jeremiah Osuna captured video footage of the red-hot lava flow, describing it as a "curtain of fire."

"It sounded like if you were to put a bunch of rocks into a dryer and turn it on as high as you could," he told Honolulu television station KOHN.

The agency said those downwind of the dissipating plume "may experience a dusting of ash," warning of "potentially lethal concentrations of sulfur dioxide gas" in the zone as well as methane blasts that could propel large rocks and debris in adjacent areas.

Governor David Ige activated the archipelago state's National Guard troops, and told residents to pay heed to warnings.

"Please be alert and prepare now to keep your family safe," Ige wrote on Twitter. Local community centers were open to residents impacted by the threat, Hawaii's emergency management agency said.

Lava spews from new ground cracks

The USGS had raised the volcano alert in the area from a watch to a warning, reporting that "new ground cracks" were discovered in the late afternoon.

"White, hot vapor and blue fume emanated from an area of cracking in the eastern part of the subdivision," the agency wrote.

It emphasised that the early stages of fissure eruptions are "dynamic," and "additional vents and new lava outbreaks may occur."

"At this time it is not possible to say where new vents" could happen, it said.

Eruptions can take place without notice

The affected area is part of the Big Island's East Rift Zone, in which the Hawaii Volcano Observatory had "identified magma movement" and warned residents that seismic activities and eruptions could take place without notice.

"All areas bordering East Rift Zone at high risk for eruption," Hawaii County's mayor Harry Kim said on Twitter.

US Senator Brian Schatz of Hawaii said The Federal Emergency Management Agency (FEMA) was mobilising resources, as well as monitoring for forest fires, power outages and water supply issues.

Hawaii Island, or the Big Island, is the largest of the eight main islands that comprise the Pacific US state, an archipelago that includes hundreds of smaller volcanic islands.

Wei, who moved to Hawaii from California - known for its high earthquake risk - said the eruption was almost a "relief".

"People live here - the Hawaiians and local people have lived here forever," she said. "You know what's going on; we have warning systems. Everybody should be prepared."

History of Kilauea volcano eruptions

Most of Kilauea's activity has been non-explosive, but a 1924 eruption spewed ash and 10-ton rocks into the sky, leaving one man dead.